Disclosed herein is a radio frequency identification (RFID) system that comprises an RFID reader and an RFID tag and performs mutual communication, and a communication method performed by the RFID system.
Radio frequency identification (RFID) technology is a radio frequency recognition technology, which identifies an object by using a radio frequency ranging, that is a radio frequency band, from MHz to GHz, without contacting the object. A wide radio frequency band makes it possible to use various types of frequencies and utilize different frequencies according to particular applications.
An RFID system using an RFID technology can be used to obtain information about a product wirelessly. For this, the RFID system includes an RFID tag that includes the information about the product and is attached to the product and an RFID reader that communicates with the RFID tag wirelessly and extracts information about the product.
In more detail, the RFID tag includes an antenna and an RFID chip, stores and renews the information sent from the RFID reader in the RFID chip through the antenna, and sends the information stored in the RFID chip to the RFID reader through the antenna. The RFID tag modulates a wireless signal sent from the antenna of the RFID reader according to the information stored in the RFID chip and reflects the modulated wireless signal. The RFID reader reads the information stored in the RFID chip from the reflected wireless signal.
RFID tags are classified into active type RFID tags and passive type RFID tags. An active RFID tag is supplied with power from outside, and thus it uses long distance communication. On the other hand, a passive RFID tag is supplied with power from a signal sent from an RFID reader, and outputs a signal that significantly changes according to a distance between the passive RFID tag and the RFID reader.
When the passive RFID tag is nearby, a high-power carrier wave is transmitted from the RFID reader to the passive RFID tag, and a modulated signal is transmitted from the passive RFID tag to the nearby RFID. On the other hand, when the passive RFID tag is far away, a low-power carrier wave is transmitted from the RFID reader to the passive RFID tag, and the modulated signal is transmitted from the passive RFID tag to the far-away RFID. That is, a signal transmitted from the passive RFID tag to the RFID reader has a power that is inversely proportional to the distance between the passive RFID tag and the RFID reader.
Also, since a passive type RFID reader aims at a long-distance recognition, receiving a signal that exceeds a certain level, e.g., from a nearby RFID tag, may cause a problem with a recognition rate of an RFID tag signal. On an experimental basis, a short-distance recognition was measured to be smaller than an appropriate distance recognition. Accordingly, the RFID reader must maintain strength of a RFID tag signal at a certain level in order to increase a recognition rate with respect to information stored in the RFID tag.